The efficacy of conventional filament light bulbs is very low—in the order of about 15 lumens per Watt. Even with the use of halogen gas to suppress vaporization of the tungsten, a maximum of about 22 lumens per Watt is anticipated. High intensity discharge (HID) can provide greater efficiency—in the order of about 75-80 lumens per Watt—as a system (including ballast losses). However, both of these conventional sources produce high temperatures, typically at the filament or arc. Moreover, both conventional sources generally have a limited life span as, for example, the filament of an incandescent bulb may be consumed, or the electrodes of an HID source may deteriorate with time and the gas within the bulb may be consumed.
Additionally, both high lumen filament and HID light sources generally share a spherical output with respect to light emission. That is, light is commonly distributed through virtually all directions. While this may be appropriate with many fixture types, there are potentially significant efficiency losses due to the optical systems generally used to manage/distribute light from such sources.
Moreover, when incandescent and HID sources operate at very high temperatures, there is the potential for burns if such source is contacted while operating or even some time after they have been extinguished. Further, HID sources may have very high starting voltages—often greater than 10,000 volts—which can pose a safety challenge.
LEDs offer a number of benefits in terms of functionality and operation. However, there are unique challenges associated with both heat and optical management. For LEDs to achieve the lumen output of traditional sources, the output of many sources are typically combined. Even though very high lumen LEDs in the order of 250-450 lumens per device have been produced, the ability of thermal systems to effectively manage the heat generated by closely spaced LEDs can present a significant challenge. Achieving comparable illumination levels to an HID source with an LED based device can present an even greater challenge.
While building interior illumination requirements may not demand high lumen levels, the exterior lighting market often demands very high lumen levels, which in part has led to the development of HID and high pressure sodium light sources. HID may represent a five-fold improvement in lighting efficiency compared with the previous technology of incandescent lighting, and high pressure sodium (HPS) may offer nearly an eight-fold improvement. While the two new technologies can offer significant lumen output, each source type may involve notable disadvantages. Each must have a weighty power supply to initiate an arc, and then a means to regulate the power to support the arc. Additionally, the time for the arc to initiate could be as high as six minutes. If a lamp where to go out and needed to be restarted, the time to regain full output could exceed 10 minutes.
HPS technology carries a further disadvantage in that the light output is monochromatic yellow since the light production is based on sodium. Color rendition of people and objects may be significantly degraded. That is, everything illuminated by an HPS light source may be virtually in one color.
High powered white LEDs can be utilized to overcome many of the disadvantages of both HID and HPS sources. Such LEDs can, inter alia, offer comparatively high efficiency, be coupled into optical systems, have very little heat projected forward, produce a broad spectrum of light, produce light substantially immediately when power is applied, have lifetimes from 3-10 times greater than HID or HPS, and retain their light output for a much longer time than the other types of light sources.
Among other things, the present invention takes into account the manner in which the benefits of LEDs may be optimized/maximized, while reducing or minimizing disadvantages that may be associated with conventional incandescent, HID and HPS sources.